In the manufacturing process of a semiconductor device or a flat panel display (FPD), a plasma is widely used in a process such as etching, deposit, oxidation, sputtering or the like since it has a good reactivity with a processing gas in a relatively low temperature. In a single wafer plasma etching apparatus, a capacitively coupled type is mainly used to generate a plasma.
An upper and a lower electrode are arranged in parallel with each other in a vacuum processing chamber included in a capacitively coupled plasma etching apparatus. Then, a target substrate (e.g., a semiconductor wafer or a glass substrate) is mounted on the lower electrode and a high frequency voltage is applied between the upper and the lower electrode. Accordingly, an electric field is generated between the electrodes by the high frequency voltage to accelerate electrons and, thus, the impact ionization occurs between the accelerated electrons and a processing gas, thereby generating a plasma. Then, a surface of the substrate is subjected to a desired etching process by radicals and ions in the plasma.
Here, since the electrode to which the high frequency voltage is applied is connected to a high frequency power supply via a blocking capacitor included in a matching unit, the electrode serves as a cathode. In a cathode coupling type in which a high frequency voltage is applied to a lower electrode as a cathode on which a substrate is mounted, ions in a plasma are attracted to the substrate in a substantial vertical direction, thereby performing an anisotropic etching with the outstanding directivity (see, e.g., Japanese Patent Application Publication No. 2000-260595).
Recently, in order to individually optimize the density of plasma and the selectivity of anisotropic etching, there has widely been employed a lower side dual frequency application type in which a first high frequency voltage having a relatively high frequency (e.g., 27 MHz or more) adequate for plasma generation and a second high frequency voltage having a relatively low frequency (e.g., 13.56 MHz or less) adequate for ion attraction are overlappingly applied to a lower electrode on which a substrate is mounted (see, e.g., Japanese Patent Application Publication No. 2000-156370 and corresponding U.S. Pat. No. 6,642,149 B2).
Moreover, in the capacitively coupled plasma etching apparatus, it is required to control the temperature of a substrate to be uniform by suppressing the increase of the temperature of the substrate caused by the heat transferred from the plasma during the plasma etching. To that end, the substrate is indirectly cooled by supplying a coolant having an adjusted temperature from a chiller unit to a coolant path provided inside the lower electrode to be circulated and a heat transfer gas such as He gas to a backside of the substrate through the lower electrode.
According to such a cooling method, a substrate holding unit is required to fixedly hold the substrate on the lower electrode against the supplying pressure of the heat transfer gas and, thus, an electrostatic chuck is mainly used as the substrate holding unit (see, e.g., Japanese Patent Laid-open Publication No. 2001-210705).
Typically, the electrostatic chuck includes a dielectric layer having a DC electrode therein which is provided on an upper surface (mounting surface) of the lower electrode and a preset DC voltage is applied to the DC electrode to attract a substrate by a Coulomb force generated between the substrate and the dielectric layer. For the electrostatic chuck, the dielectric layer has recently been made of alumina ceramic (Al2O3) having high plasma resistance and high heat resistance.
Meanwhile, in the capacitively coupled plasma etching apparatus, some of gaseous reaction products or by-products produced during the plasma etching are attached to members inside the chamber, especially, an upper electrode, a focus ring, a sidewall of the chamber and the like, which face a plasma generation space or a processing space, to be solidified into deposits.
As such, if the deposits attached to the members in the chamber are detached therefrom by being, e.g., peeled off, particles are generated, thereby decreasing the yield of devices. Accordingly, a cleaning process is regularly performed to remove the deposits from the members in the chamber. Such kinds of cleaning processes are classified into two groups, i.e., a gas cleaning performed by a thermal decomposition of gas and a plasma cleaning performed by decomposing a cleaning gas by a plasma.
When the plasma cleaning is performed, in the cathode coupling type, a high frequency voltage for plasma generation is applied to the lower electrode as in the dry etching process. In the lower side dual frequency application type, the second high frequency voltage for ion attraction is not applied and only the first high frequency for plasma generation is applied to the lower electrode. The cycle of the regular plasma cleaning is may be carried out lot by lot. However, it is preferable that the cycle is carried sheet by sheet to reliably prevent the influence of deposits on the process.
However, in the conventional capacitively coupled plasma etching apparatus, whenever the plasma cleaning is performed, a (dielectric) top surface portion of the electrostatic chuck is slightly eroded by an ion sputtering effect. Accordingly, as the plasma cleaning is repeatedly performed, such erosion is progressed, shortening the lifespan of the electrostatic chuck. Furthermore, when the dielectric portion of the electrostatic chuck is made of a metal, especially, e.g., alumina ceramic (Al2O3), the aluminum is scattered as particles or compounds (e.g., Al fluoride or Al chloride) in the chamber due to the erosion and some of the particles or the compounds is remain without being not exhausted. Such particles or compounds are attached to a substrate subjected to the etching process, thereby causing the metal contamination.
In addition, when the plasma cleaning is performed, only the high frequency voltage for the plasma generation is applied to the lower electrode. Nevertheless, a self bias voltage is unavoidably generated and an ion sheath is formed between the plasma and the lower electrode. Accordingly, ions in the plasma are accelerated by an electric field inside the ion sheath to be incident on the (dielectric) top surface portion of the electrostatic chuck, causing the dielectric material to sputter.
To prevent the metal contamination caused by the electrostatic chuck, a deposition creating process is performed by supplying a film formation gas, e.g., SiCl4 gas, to the chamber after the plasma cleaning to coat the surface of the electrostatic chuck with a thin film made of SiClxOy or the like in the conventional capacitively coupled plasma etching apparatus. However, such a method requires expensive equipment such as gas structure for the depositing process and a prolonged post-processing, so that it is difficult to use the method.